Monitoring liquid characteristics including quality control

ABSTRACT

A drilling mud monitoring system includes a single measurement chamber which is filled with a predetermined quantity of drilling mud. The chamber is weighed to provide a value representative of the density of the drilling mud. The time needed for the chamber to drain is measured to provide a value representative of viscosity. The system proceeds through a measurement cycle in which the chamber is filled, weighed, timed and washed. At the end of the wash step, the weight of the chamber is compared with an empty weight and if the chamber weighs too much, the conclusion is that drilling mud adheres to the chamber so it is washed again. An alarm is sounded if the mud weight is too low and/or too high or in the case of a machine malfunction.

[0001] This application is a divisional application of U.S. applicationSer. No. 09/655,048, filed Sep. 5, 2000, entitled AUTOMATICALLYMONITORING DRILLING MUD.

[0002] This invention relates to a method and apparatus forautomatically monitoring the density and viscosity of a liquid, such asdrilling mud.

BACKGROUND OF THE INVENTION

[0003] Drilling fluids used to drill wells into the earth are commonlycalled drilling muds because the original drilling fluid was simplywater that mixed with clays in the earth to produce a thin natural mud.Typically, drilling mud is pumped down the drill string, through nozzlesin the end of the bit and then upwardly in the annulus between the drillstring and the wall of the bore hole. Drilling mud has a variety offunctions and must accordingly have comparable capabilities. Cuttingsgenerated by the bit are moved away from the bottom of the hole and thenupwardly through the annulus to the surface to present a clean rock faceto be drilled. The bit is cooled and lubricated by the drilling mud. Themud also forms a wall cake on the exposed face of the well bore toprevent the drilled formations caving into the bore hole. The pressureof fluids in the formations penetrated by the bit is counterbalanced, orat least partially so, by the hydrostatic weight of the mud column inthe hole. The drilling mud is modified to prevent undue effects on thebore hole wall, e.g. to prevent shale swelling. In water based muds,materials are added to prevent undue water loss into permeableformations penetrated by the bit. Various materials are added to reducefriction between the drill string and the bore hole wall. An almostendless list of substances have been added to drilling mud for a varietyof reasons.

[0004] Two important characteristics of drilling mud are mud weight andviscosity. Mud weight is important to counterbalance the pressure inpermeable formations penetrated so the well does not blow out. InEnglish measurement systems, mud weight is reported in pounds pergallon. Most wells are drilled overbalanced, i.e. the mud weight issufficient to contain formation pressures. Some wells are drilledunderbalanced, i.e. the mud weight is not sufficient to wholly containformation pressures, so the contents of drilled formations flow into thebore hole and are circulated to the surface. When it is desired to drilloverbalanced, mud weights that are too low cause a well to kick or blowout. When it is desired to drill overbalanced, mud weights that are toohigh normally produce only unnecessary costs although there is a slightdanger of causing formations up the hole to break down and take mud.When it is desired to drill underbalanced, mud weights that are too lowcreate an excessive pressure differential across the formation face.When it is desired to drill underbalanced, mud weights that are too highmay result in drilling the well overbalanced. In any event, abruptchanges in mud weight are a reliable signal that something is amiss and,in some situations, is a sign that disaster is approaching.

[0005] Mud weight is conventionally measured with a beam balance havinga small metal cup at one end receiving a fixed amount of mud and asliding weight on a lever arm fixed to the cup. The beam is placed on apivot and the sliding weight moved along the lever arm until itbalances. The density of the mud is read off the lever arm adjacent theslide. Mud weight is controlled by the addition of weight materials tothe mud, usually barite which is a naturally occurring barium sulfate orhematite which is an iron oxide.

[0006] Viscosity of drilling mud is important because it is a measure ofthe capacity of the mud to move cuttings up the hole and a measure ofthe gel strength of the drilling mud which is related to the thixotropiccapacity of the mud, i.e. the ability to set up as a gel or semi-solidthereby suspending cuttings to prevent them from settling to the bottomof the bore hole when the mud is quiescent. Viscosity is conventionallymeasured by adding a predetermined quantity of mud to a funnel ofpredetermined shape, known as a viscosimeter, Saybolt funnel orviscosity funnel, allowing the predetermined volume to run out of thefunnel and measuring the time for the funnel to empty. Viscosity ofdrilling mud is typically measured in seconds. With low cost, waterbased muds, viscosity is controlled by the addition of bentonite whichis often called gel. Bentonite is a naturally occurring swellable clayand has been used for decades as the standard viscosifier in drillingmuds. Many other materials, such as polymers, are also commonly used.

[0007] Drilling mud has many other properties that are measured by atechnician known as a mud man. These properties include water loss, pH,gel strength, and the like. Although these properties are of importancefor a variety of different reasons, to the drilling contractor or personresponsible for drilling the well and delivering a logable hole at theleast cost, the most important mud characteristics are mud weight andviscosity.

[0008] It is known in the art to automatically monitor mud weight and/orviscosity of drilling mud as shown in U.S. Pat. Nos. 2,132,015;2,252,014; 3,074,266 and 5,052,219.

SUMMARY OF THE INVENTION

[0009] In this invention, an automated device is provided toperiodically measure the density and viscosity of any suitable liquid,such as solutions, slurries or suspensions of any type, for exampledrilling mud, paint, and the like. Although the method and apparatus ofthis invention are applicable to other liquids, this invention isdescribed in conjunction with drilling mud because that is a particularniche for which the invention has application.

[0010] A suitable print out is provided, preferably at a remotelocation, such as the driller's station, a central office or a locationhandy to a drilling consultant. An important feature of this inventionis using a single container to weigh a quantity of mud and measure thetime it takes for the mud to drain out of the container therebyproviding a measure of viscosity.

[0011] A variety of features allow the device of this invention toproduce consistently reliable results: (1) the measuring container iswashed at the end of every measurement cycle and, if the weight of thecontainer does not fall to a predetermined empty weight, the containeris rewashed; (2) if rewashing does not reduce the weight of thecontainer to its empty weight, the conclusion is that mud solids haveadhered to the container which can corrupt subsequent measurements andan alarm is accordingly sounded and the device turned off; (3) an alarmis sounded if the mud weight measures a value which is too low and/ortoo high; (4) the too low weight and/or the too high weight limits canbe set by an operator; (5) in the event the measuring containeroverflows, the device is shut off and an alarm sounded; (6) when thesupply valve to the mud container opens, the weight of the container ismonitored so that, if the weight of the container does not increase, theconclusion is made that something is amiss with the supply valve and/orthere is a blockage in the mud line; (7) multiple weight measurementsare taken and then averaged to provide the reported mud weight; and (8)a relatively large volume of mud is weighed, as compared to theconventional beam balance thereby providing greater accuracy becausesmall errors are not magnified by the multiplication that necessarilygoes on to convert the measured value to pounds per gallon.

[0012] It is an object of this invention to provide an improved methodand apparatus for automatically monitoring drilling mud.

[0013] Another object of this invention is to provide a method andapparatus for measuring the density and viscosity of drilling mud.

[0014] A further object of this invention to provide apparatus formonitoring drilling mud which is inexpensive and reliable and whichproduces consistent results.

[0015] Another object of this invention is to provide an apparatus formeasuring drilling mud weight and viscosity which employs a singlemeasuring container.

[0016] These and other objects and advantages of this invention willbecome more fully apparent as this description proceeds, reference beingmade to the accompanying drawings and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 is an isometric view of the apparatus of this invention;

[0018]FIG. 2 is an enlarged cross-sectional view of the device of FIG.1, taken substantially along line 2—2 as viewed in the directionindicated by the arrows; and

[0019]FIG. 3 is a front view of a recorder used with this invention.

DETAILED DESCRIPTION

[0020] Referring to FIGS. 1-2, a mud monitoring device 10 of thisinvention comprises, as major components, a housing 12, a chamber orfunnel 14 for receiving a quantity of drilling mud, means 16 fordelivering a predetermined quantity of mud to the chamber 14, means 18for weighing the chamber 14, means 20 for washing the chamber 14 andmeans 22 for controlling operation of the device 10 including monitoringthe weighing means 18 and measuring the time for the chamber 14 todrain.

[0021] The housing 12 is of conventional design and includes a metallicor plastic box having a door 24 mounted for pivotal movement on an axis26. A suitable latch or lock (not shown) releasably attaches the door ina closed position.

[0022] The chamber 14 is preferably in the shape and size of a standardSaybolt or viscosity funnel conventionally used to measure drilling mudviscosity. A standard Saybolt or viscosity funnel has a generallyfrustoconical shaped side or bottom wall 28, has an outlet 30 providingan opening 32 that is 0.180 inches in inside diameter, is 14.25 inchestall and has a slope of 14°. In a conventional viscosity measuringtechnique, one quart of liquid is poured into the funnel 14 with afinger closing the outlet opening 32. The user would remove the fingerfrom the outlet opening 32 and measure the time, usually with a wristwatch, needed for the funnel 14 to empty.

[0023] Ideally, the chamber 14 is a standard Saybolt or viscosity funnelin which the handle 34 is attached to an element 36 of the weighingmeans 18 by fasteners 38 as will be described more fully apparenthereinafter. Using the standard Saybolt or viscosity funnel as theweighing chamber 14 is an ideal approach because the viscosity of thedrilling mud can be determined simply by measuring the time for thefunnel to drain which is necessarily part of the weighing cycle.

[0024] The mud delivery means 16 includes a conduit 40 connected to amud line of the drilling rig (not shown) with which this invention isused. Desirably, the monitoring device 10 is placed in the mud lineleading from the well and a second monitoring device is placed in themud line leading to the well. In this manner, mud weight and viscosityare measured after the mud is treated and before it is pumped into thewell and after the mud exits from the well. The device 10 that measuresmud coming from the well is preferably placed upstream of any shaleshaker or the like where treatment of the mud affects mud weight and/orviscosity. When placed upstream from the shale shaker, it is desirableto provide a screen through which the liquid mud flows to the device 10while allowing large solids to bypass the device 10, as will be pointedout more fully hereinafter.

[0025] When the control means 22 starts a measurement cycle, a signal issent to a valve motor 42 which opens a valve 44 thereby deliveringdrilling mud through an outlet 46 into the funnel 14. Because mud flowinto the funnel 14 is much greater than mud flow out of the opening 32,the funnel 14 fills. The rate of filling is the difference between theinflow rate through the valve 44 and the outflow rate through theopening 32. When the liquid in the funnel 14 reaches a predeterminedlevel, the controller 22 sends a signal to the valve motor 42 to closethe valve 44. The liquid level in the funnel 14 is sensed by a sensor 50of any suitable type providing a signal to the controller 22 over outletwires 52 which conveniently pass through a metallic support 54supporting the sensor 50. The sensor 50 may be a float operated switch,an ultrasonic liquid level detector or the like. The support 54 may beadjustable to provide a means of adjusting the position of the sensor50.

[0026] The weighing means 18 includes an L-shaped support 56 to whichthe chamber 14 is fixed. The support 56 includes the vertical element 36to which the funnel handle 34 is fixed and a horizontal element 60having an passage 62 opening through the forward edge of the element 60.The lower end of the funnel 14 extends through the passage 62 and can beremoved by deforming the plastic body of the lower end of the funnel 14and pulling it through the passage 62. The support 56 is mounted on anarm 64 extending upwardly from a horizontal wall 66 for pivotal movementabout an axis 68. The free end of the horizontal element 60 isaccordingly mounted for movement between an operative position abuttinga load cell 70 which senses the load applied by the support 56, theempty funnel 14 and any drilling mud in the funnel. The load cell 70connects to the controller 22 by suitable wires 72.

[0027] A lock out mechanism 74 is provided to support the element 60 outof contact with the load cell 70 to allow the device 10 to betransported without damaging the load cell 70. The mechanism 74accordingly includes a rigid body 76 having a slot 78 of a size toreceive the end of the horizontal element 60. The body 76 is mounted forrotational movement about a vertical axis 80 so the slot 78 moves to aposition out of engagement with the element 60 allowing the device 10 tooperate and into a position supporting the element 60 thereby preventingdamage to the load cell 70 during handling.

[0028] The washing means 20 includes a conduit 82 connected to a sourceof relatively clean wash liquid, such as water or diesel fuel, as isavailable on any drilling rig. Water is used as the wash liquid when themud is a water based mud and diesel fuel is used when the mud is an oilemulsion. A spray nozzle 84 is positioned below the top of the funnel 14and above the level of liquid sensed by the sensor 50 to start weighingand viscosity measurements. The nozzle 84 delivers a large quantity ofclean wash liquid to rinse and thereby clean the inside of the funnel14. The washing means 20 is controlled by a suitable valve 86 operatedby a solenoid or other conventional operator receiving a signal alongwires 88 from the controller 22.

[0029] A description of the operation of the device 10 reveals a numberof important features. It is preferred that the drilling mud bemonitored at relatively frequent intervals, e.g. every fifteen minutes.The time between measurement cycles can be incorporated into thecontroller or may be set in the field in any suitable fashion, as by aninput (not shown) on the controller 22 or on a recorder 92.

[0030] At the beginning of a measurement cycle, a signal passes from thecontroller 22 to the valve motor 42. Because the funnel outlet opening32 is restricted, the funnel 14 fills rather rapidly and is notparticularly flat. For this reason, the sensor 50 detects a risingliquid level in the funnel 14 and the controller 22 closes the valve 44in response to the rising liquid level. Because of the time delay andbecause of the volume of liquid in the outlet 46 downstream of thevalve, the liquid level in the funnel 14 rises slightly after the sensor50 detects the liquid level which is selected to shut off the valve 44.After flow into the funnel 14 stops, the liquid surface in the funnel 14flattens out and relatively slow flow through the funnel outlet 30causes the liquid surface to become reasonably flat. As the liquid levelin the funnel falls, the sensor 50 detects a predetermined value whichis recognized by the controller 22 and used to initiate weighing.

[0031] Modern load cells are capable of making a large number ofmeasurements in a very short time, e.g. one hundred measurements in ananosecond. In a nanosecond, very little liquid flows through therestricted outlet opening 32 so a large number of measurements can bemade and averaged. Preferably, values which are abnormally high or lowcan be discarded before averaging the balance. Ideally, the high 5% ofthe measured values and the low 5% of the measured values are discardedand the balanced averaged to provide a measurement which is transmittedby the controller to a suitable display 94 on the recorder 92 throughwires 96 or through a wireless transmitter (not shown). The recorder 92may be of any suitable type and one may be located at the driller'sstation, in a central office location or in a trailer or other locationsuitable for a drilling consultant.

[0032] An important feature of this invention is measuring the chamber14 when it is empty which is included to mean when it is dry or when itis water wet. This measurement is necessary to determine the density ofthe mud being monitored because one gets a value from the load cell 70representative of a full weight and a deduction needs to be made for anempty weight.

[0033] The liquid level sensed by the sensor 50 to measure the weight ofthe mud in the funnel 14 is conveniently but not necessarily used tomeasure viscosity. In other words, the liquid level sensed by the sensor50 as mud is running out of the funnel is the liquid level correspondingto the predetermined volumetric capacity, e.g. one quart, in the funnel.It should be understood, of course, that different liquid levels couldbe used for weight and viscosity measurements with the necessaryadjusting calculations being made by the controller 22. Viscosity isaccordingly simply measured by measuring the time needed for the weightof the funnel to fall from the full weight to the empty weight. In theevent the measured weight of the funnel does not fall to the emptyweight within a reasonable time, e.g. two minutes, the conclusion isthere is some reason the funnel has not emptied, such as a shaleparticle stuck in the outlet opening. The washing means 20 is turned onto rinse the funnel and the measuring cycle is repeated before recordingany of the values. In the event the empty weight on the next measuringcycle does not fall to the empty weight within a reasonable time, analarm 98 at the recorder 92 is sounded, a message is printed out at therecorder 92 and the device 10 turned off.

[0034] By weighing the funnel 14 when it contains a predetermined largevolume, e.g. one or more quarts, the density of the mud in pounds pergallon is obtained simply by multiplying the difference between the fullweight and empty weight of the funnel by a factor which is sufficient toraise the volume to a gallon. A preferred volume for the funnel 14 isone quart, which is the volume necessary for a conventional viscositymeasurement. The factor necessary to raise the volume to a gallon isaccordingly four. Thus, any error in the weighing operation ismagnified, using the preferred volume of one quart, only by a factor offour. In a conventional mud weighing balance, the cup capacity is onlyabout four fluid ounces so the multiplication factor is thirty two.Thus, any measurement error in a conventional mud balance is magnifiedto a much greater extent than in this invention.

[0035] If viscosity is successfully measured, the date, time of day, mudweight and viscosity are printed out on a paper 100 exiting from therecorder 92.

[0036] At the end of a successful measurement cycle, the controller 22turns on the washing means 20 to rinse away any drilling mud on theinside of the funnel 14. The load cell 70 continually measures the loadon the horizontal element 60 in the sense that the element 60continually bears on the load cell 70. Thus, the weight of the funnel ismeasured at the end of the wash cycle. In the event the weight of thefunnel 14 returns to the empty weight, the conclusion is that the funnelis clean and the device 10 is ready for another measurement cycle. Inthe event the weight of the funnel does not fall to the empty weight,the conclusion is that the funnel contains some drilling mud residue andthe washing means 20 is turned on again. If the weight of the funnelreturns to the empty weight, the conclusion is that the funnel is cleanand the device 10 is ready for another measurement cycle. In the eventthe weight of the funnel again does not fall to the empty weight, amessage to this effect is printed on the paper 100 by the recorder 92,the alarm 98 is sounded and the device 10 is turned off.

[0037] The device 10 is capable of setting off the alarm 98 in the eventmud weight falls too low or becomes too high. Ideally, this value may beset at the recorder 92 by an input 102.

[0038] The device includes other features promoting consistentlyreliable results. In the event the funnel 14 overflows, this conditionis detected because the weight of the funnel increases to a point andthen stops at a time when the valve 44 is open and the sensor 50 has notyet indicated that the predetermined level is reached. The conclusion isthat the sensor 50 has malfunctioned so the alarm 98 is sounded, amessage is printed on the paper 100 and the device 10 is turned off.

[0039] When the supply valve 44 is open and the weight of the containerdoes not increase, the conclusion is that something is amiss with thesupply valve and/or there is a blockage in the conduit 40, or in ascreen assembly 104 through which mud flows into the conduit 40 or thatmud flow has stopped for a substantial time for some other reason. Aftera delay of a few minutes, a message is printed on the paper 100 and thealarm 98 sounded. To avoid sounding the alarm during an intendedinterruption of mud flow, as when making a connection, several optionsare feasible. The conduit 40 may connect to part of the mud system wherean accumulation of mud exists, e.g. to the inlet box of a shale shaker.In the alternative, a connection may be made from the controller 22 tothe rig pumps so that when the rig pumps are stopped, no measurementsare taken.

[0040] Referring to FIGS. 1-2, a screen assembly 104 is provided toremove drilled solids, such as large shale particles, from the mudupstream of the device 10. The screen assembly 104 comprises a tee 106in the conduit 40, an inclined screen 108 in the tee, and a drain 110leading off from the tee 106 providing a restricted drain hole 112. Whenthe supply valve 44 is closed, mud passes through the tee 106, throughthe drain 110 and out through the drain hole 112. When the supply valve44 opens, mud flows through the screen 108. Any large particles arerejected by the screen 108 and drop into the drain 110. It would appearthat mud located between the tee 106 and the valve 44 is old mud and itspresence would affect readings taken by the device 10. In practice, thevolume of mud in the line 40 between the valve 44 and the tee 106 isvery small and it flows out of the bottom of the funnel 14 well beforeany measurements take place. At the end of a measurement cycle, a supplyof wash liquid is delivered through a conduit 114 to wash any drilledsolids collecting on the screen back into the drain 110.

[0041] When the valve 44 is closed, all flow toward the device 10 isdiverted to the drain 110. When the valve 44 opens, almost all flow isdiverted to the device 10 because the restricted drain opening 112provides a much greater restriction to flow than does the valve 44 andpiping downstream of the screen assembly 104.

[0042] Although this invention has been disclosed and described in itspreferred forms with a certain degree of particularity, it is understoodthat the present disclosure of the preferred forms is only by way ofexample and that numerous changes in the details of operation and in thecombination and arrangement of parts may be resorted to withoutdeparting from the spirit and scope of the invention as hereinafterclaimed.

I claim:
 1. An apparatus for monitoring density and viscosity of aliquid, comprising a measuring container for receiving the liquid; aninlet for connection to a source of the liquid and having a valve forfilling the container; an assembly for obtaining the weight of thecontainer and thereby obtaining a value representative of the density ofthe liquid including an assembly for obtaining a weight of the containera multiplicity of times; an assembly obtaining a value representative ofthe viscosity of the liquid; and an assembly for conducting qualitycontrol determinations using the multiplicity of weights of thecontainer.
 2. The apparatus of claim 1 wherein the assembly forobtaining a weight of the container a multiplicity of times comprises anassembly for obtaining the weight of the container a multiplicity oftimes during filling of the container and the quality controldetermination assembly comprises an assembly for conducting qualitycontrol determinations during filling.
 3. The apparatus of claim 2wherein the quality control determination assembly comprises an assemblymeasuring the weight of the container at a time when the valve is open.4. The apparatus of claim 2 wherein the quality control determinationassembly comprises an assembly measuring the weight of the container ata time when the valve is closed.
 5. The apparatus of claim 1 furthercomprising an assembly for rinsing the container after weighing thecontainer and an assembly for comparing the weight of the containerafter rinsing with an empty weight of the container and activating therinsing assembly again if the weight of the container is more than theempty weight.
 6. The apparatus of claim 5 further comprising an assemblyfor comparing the weight of the container after a subsequent rinsing ofthe container and sounding an alarm if the weight of the container ismore than the empty weight.
 7. An apparatus for monitoring density andviscosity of a liquid, comprising a measuring container for receivingthe liquid; an assembly for obtaining the weight of the container andthereby obtaining a value representative of the density of the liquid;an assembly obtaining a value representative of the viscosity of theliquid; an assembly for rinsing the container after weighing thecontainer; an assembly for comparing the weight of the container afterrinsing with an empty weight of the container and activating the rinsingassembly again if the weight of the container is more than the emptyweight.
 8. The apparatus of claim 7 comprising an assembly for comparingthe weight of the container after a subsequent rinsing of the containerand sounding an alarm if the weight of the container is more than theempty weight.
 9. An apparatus for monitoring the density and viscosityof a liquid, comprising a measuring container for receiving the liquid;an inlet for connection to a source of the liquid for filling thecontainer; a container disposed to receive the liquid from the inlet; anassembly for obtaining the weight of the container and thereby obtaininga value representative of the density of the liquid including anassembly for weighing the container during filling; an assemblyobtaining a value representative of the viscosity of the liquid; anassembly for turning off the apparatus in the event the weight of thecontainer does not increase at a time when the valve is open.
 10. Anapparatus for monitoring density and viscosity of a liquid, comprising ameasuring container for receiving the liquid; an inlet for connection toa source of the liquid for filling the container; an assembly forobtaining the weight of the container and thereby obtaining a valuerepresentative of the density of the liquid including an assembly forweighing the container during filling; an assembly obtaining a valuerepresentative of the viscosity of the liquid; an assembly fordetermining if the container overflows; and an assembly for turning offthe apparatus in response to the determining assembly in the event thecontainer overflows.
 11. The apparatus of claim 10 further comprising avalve in the inlet and wherein the determining assembly comprises anassembly for determining if the weight of the container rises and thenbecomes constant at a time when the valve is open.